1. Field of the Invention
The present invention relates to a communication device connected to a telephone line together with a telephone set. More specifically, the present invention relates to a communication device such as a video telephone whose operation mode can be controlled in response to a control signal supplied from a telephone set.
2. Description of the Prior Art
One example of a conventionally known communication device to be controlled in response to a control signal outputted from a telephone set is disclosed in, for example, Japanese Patent Application Laid-open No. 204162/1985. In this prior art, a communication device such as a facsimile is connected to a telephone line together with a telephone set and the facsimile is controlled in response to a control signal supplied from the telephone set. More specifically, the facsimile is driven when the specified number is entered from the telephone set after being connected to the telephone line, thereby to control a receiving or transmitting operation of the facsimile.
In the above described prior art, the facsimile does not have a function for determining whether a control signal being transmitted onto the telephone line is transmitted in an upward direction of the telephone line or in a downward direction of the telephone line. Accordingly, in a case where the facsimile is controlled under the leadership of a calling subscriber's telephone set, when a called subscriber erroneously transmits a control signal, the facsimile is liable to be erroneously operated in response to the erroneous operation of the called subscriber's telephone set. In addition, in order to remotely control such a communication device, the telephone line must be necessarily connected thereto.